Discontinuity in the responses of ecosystem processes and multifunctionality to altered soil community composition

Abstract

Ecosystem management policies increasingly emphasize provision of multiple, as opposed to single, ecosystem services. Management for such "multifunctionality" has stimulated research into the role that biodiversity plays in providing desired rates of multiple ecosystem processes. Positive effects of biodiversity on indices of multifunctionality are consistently found, primarily because species that are redundant for one ecosystem process under a given set of environmental conditions play a distinct role under different conditions or in the provision of another ecosystem process. Here we show that the positive effects of diversity (specifically community composition) on multifunctionality indices can also arise from a statistical fallacy analogous to Simpson's paradox (where aggregating data obscures causal relationships). We manipulated soil faunal community composition in combination with nitrogen fertilization of model grassland ecosystems and repeatedly measured five ecosystem processes related to plant productivity, carbon storage, and nutrient turnover. We calculated three common multifunctionality indices based on these processes and found that the functional complexity of the soil communities had a consistent positive effect on the indices. However, only two of the five ecosystem processes also responded positively to increasing complexity, whereas the other three responded neutrally or negatively. Furthermore, none of the individual processes responded to both the complexity and the nitrogen manipulations in a manner consistent with the indices. Our data show that multifunctionality indices can obscure relationships that exist between communities and key ecosystem processes, leading us to question their use in advancing theoretical understanding-and in management decisions-about how biodiversity is related to the provision of multiple ecosystem services.aboveground-belowground interactions | ecosystem functioning | plant-soil feedbacks | soil biodiversity | soil fauna

Biotic homogenization can decrease landscape-scale forest multifunctionality

“…Multifunctionality can be measured by a variety of methods, and the most appropriate means of doing so remains unresolved (24)(25)(26)(27), particularly at larger scales, where the desired distribution of ecosystem function across the landscape has not been quantified. At local scales, one can quantify ecosystem multifunctionality as the number of ecosystem functions that exceed a given threshold value, where the threshold equals a certain percentage of the maximum observed value of each function (10, 24) (hereafter "threshold-based multifunctionality"; Fig.…”

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

“…The abundance and biodiversity of soil organisms is reduced as a result of intensive grazing, biomass burning (either of crop residue or for land clearing) [87], tillage and bed preparation [88], leaving soils bare, mono-cropping, especially in maize growing areas, and excess fertilizer application [82,89]. Such changes in the soil diversity (or functional diversity) of soil biota can affect the availability of nutrients [90,91] and alter pest and disease pressure [81] as well as the complexity of food-webs [81] with consequences for ecosystem resilience.…”

Functional traits in agriculture: agrobiodiversity and ecosystem services

“…The effects of biodiversity on multifunctionality are often context dependent, because different mechanisms govern different ecosystem processes [27]. Therefore, managing for multiple agroecosystem services requires understanding the responses of individual services to changes in environment and management as well as trade-offs that exist among services [27,28].…”

“…The effects of biodiversity on multifunctionality are often context dependent, because different mechanisms govern different ecosystem processes [27]. Therefore, managing for multiple agroecosystem services requires understanding the responses of individual services to changes in environment and management as well as trade-offs that exist among services [27,28]. Given its mechanistic foundation, a traitbased approach could be used to develop agricultural and land-use management strategies to provide multiple ecosystem services that take into account such trade-offs (see the section 'Using traits to generate ecosystem management strategies').…”